1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object, and, in particular, to an active type rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a CPU. Namely, an integrating capacitor charged with a reference voltage V.sub.REF is discharged by a voltage value corresponding to the distance information signal. As a consequence, the voltage of the integrating capacitor decreases stepwise (C.sub.INT in FIG. 1: first integration) as the distance information signal is inputted every time the IRED emits light (when the INT signal in FIG. 1 is HIGH). Thereafter, the integrating capacitor is charged at a constant rate determined by the rating of a constant current source (C.sub.INT in FIG. 1: second integration). Then, the time required for the second integration is measured, and the distance to the object is detected according to thus measured time.